Binders or binder systems for foundry cores and molds are well-known. In the foundry art, cores or molds for making metal castings are normally prepared from a mixture of an aggregate material, such as sand, and a binding amount of a binder or binder system. Typically, after the aggregate material and binder have been mixed, the resulting mixture is rammed, blown or otherwise formed to the desired shape or pattern, and then cured with the use of catalysts and/or heat to a solid, cured state.
A variety of different processes for forming molds and cores have been developed in the foundry industry. One type of process known as the "hot-box" process requires that the mixture of aggregate material and binder be cured and hardened in a holding pattern or core box while subjected to heat. Another type of binder system which does not require heating in order to bring about curing or hardening is known as a "no-bake" process. A third type of process used for forming molds or cores is known as the "cold-box" process. Cold-box processes are generally carried out by passing gaseous catalysts or hardeners through molded resin-coated sand at ambient temperatures in order to achieve curing.
One such "cold-box" process employs an aqueous alkaline solution of a phenolic resole resin as the binder. This binder is cured by passing the volatile ester through the molded resin-coated material. The process is described in detail in U.S. Pat. No. 4,468,359 (Re. 32,720).
The ester cured process is superior to some of the earlier processes from an environmental standpoint. However, sands coated with alkaline phenolic resole resins tend to have less flowability than sands coated with certain other binder systems. This can adversely affect quality of the foundry cores and molds. In the case of this cold-box process, higher blow pressures are needed to blow the coated sand into the core boxes and it is more difficult to blow uniformly dense cores.
Now it has been found, in accordance with this invention, that when certain compounds are used with the ester-curable alkaline phenolic resole resin binders, they improve greatly the flowability of sands coated with the binders. These sands form cores and molds with smoother surfaces and sharper edges, as well as with more uniform density. Such cores and molds give castings of better quality. This improvement also makes possible the production of cores and molds with more delicate patterns. Furthermore, when the resin coated sands of this invention are blown into core boxes, they can be blown at lower pressures resulting in less pattern wear and in less sand being blown out of the vents. In addition, the cores prepared from these sands are released more readily from the core boxes.